1. Field of the Invention
The present invention relates to an image forming apparatus and, more specifically to a technique for extracting a hand-written image.
2. Description of the Background Art
Conventionally, many techniques have been proposed for extracting image data based on an image written by hand (hereinafter referred to as “hand-written image”) using a pen or the like on an original image from image data of original image and performing various image processing operations including erasure and emphasis on the extracted image data.
By way of example, Japanese Patent Laying-Open No. 2005-175565 (hereinafter referred to as “'565 application’”) discloses a technique in which a line segment of a prescribed length or longer of an input image data and a color spectrum of the line segment are detected, for discriminating a part of the image data having the same color spectrum as the detected line segment to be an original part, and a part having a different color spectrum to be a hand-written part.
Further, Japanese Patent Laying-Open No. 2005-167875 (hereinafter referred to as “'875 application’”) discloses a technique in which a copy image is read and an area surrounded by a half-tone line segment written by hand using a marker or the like on the copy image is recognized, and of the original image data stored beforehand in an image forming apparatus, image data on the inside or outside of the area corresponding to the recognized area is subjected to processes such as trimming or masking.
According to the technique disclosed in '565 application, when the color spectrum of the original image is distinctively different from the color spectrum of the hand-written image, for example, when a hand-written image is written with red ink on a black-and-white image, the position of hand-written part can accurately be discriminated. On the other hand, if the color spectrum of the original image and the hand-written image are intricate, for example, when a hand-written image is written on a color image or when hand-written images are written using pens of different colors on the original image, erroneous discrimination may be possible.
According to the technique disclosed in '875 application, if a user wishes to extract a desired area, he/she must draw a line surrounding the desired area using a marker or the like. Therefore, if a hand-written image is to be erased, for example, it is necessary to additionally draw a hand-written surrounding line. Further, if the hand-written area and the original image are mixed in an intricate manner, the task of forming the surrounding line itself is difficult and impractical.